Conventionally, a method of controlling combustion in an internal combustion engine of a vehicle or the like is known (see, for example, Japanese Examined Patent Application, Second Publication No. H04-15388) in which the quantity of fuel that is injected is controlled so as to match the quantity of air that is taken in from the outside, and a mixture of air and fuel is ignited and combusted in accordance with the angle of rotation of the crankshaft.
Here, the technology that controls this fuel injection is disclosed in the aforementioned document. Specifically, a structure is employed to control the fuel injection into a multi cylinder engine in which a flow rate sensor is provided on an air intake passage between a throttle valve and an electromagnetic injection valve. A control circuit calculates a basic fuel injection quantity at predetermined timings based upon an average value of the flow rate of the intake air that is detected by the flow rate sensor. Fuel injection is then performed based on this basic injection quantity. The cylinders performing the air intake switch in sequence during one engine cycle. Variations in the intake air flow rate that are generated at this time are taken as deviations from the average value of the intake air flow rate, and deviation signals corresponding to these deviations are input directly into a voltage circuit of the electromagnetic injection valve. The fuel injection quantity is increased when there is a large deviation signal, and is decreased when there is a small deviation. For this calculation of the basic fuel injection quantity, compensation is performed using an air intake temperature sensor that detects the temperature of the air that is taken in and a cooling water temperature sensor that detects the temperature of the engine cooling water.
In order to improve combustion efficiency and response, it is desirable that the quantity of air that is actually taken into an internal combustion engine is measured at each intake, and that the optimal fuel injection quantity be determined for each air intake quantity. It is also desirable that the fuel injection is performed while the air intake valve is open and air is flowing. However, because the final fuel injection quantity is determined after the air intake valve has closed, if the fuel injection quantity is determined after the air quantity until the air intake has ended has been calculated, it is not possible to inject fuel while the air intake valve is open. If the fuel injection for an intake stroke is continued even after the air intake valve has been closed, the quantity of fuel in the fuel-air mixture that is supplied to the interior of the engine in the intake stroke is decreased. As a result, the air-fuel ratio becomes disproportionate. Moreover, because fuel remains inside the air intake manifold, the quantity of fuel in the fuel-air mixture that is supplied to the interior of the engine in the next intake stroke is increased, so that again the air-fuel ratio becomes disproportionate.
Accordingly, the present invention was conceived in order to solve the above described problems, and it is an object thereof to provide a control unit for an internal combustion engine that has a simple structure and enables a required quantity of fuel to be injected at an appropriate timing.